1. Field of the Invention
This invention relates in general to an engine mount, and relates in particular to an engine mount having an integrally disposed vibration damping bushing at a location between a pair of block shaped rubber mount elements.
2. Description of the Related Art
One type of engine mount known to date is furnished with a metallic upper fitting and a metallic lower fitting of plate shape, and a pair of integrally vulcanization bonded rubber mount elements of block shape, sandwiched above and below by the upper fitting and a lower fitting. However, in the case of an engine mount of this design, there is the problem that when a constant spring constant in the vertical direction is established for the purpose of properly supporting the engine load or properly exhibiting vibration damping characteristics, the spring constant in the vehicle front-back direction or left-right direction is insufficient.
To solve this problem, JP-A-2001-3987 cited below, it is proposed to integrally attach a vibration damping bushing to a mount body comprising the pair of block shaped rubber mount elements discussed previously. A specific example thereof is depicted in FIGS. 10A and 10B. In the drawing, 200 denotes the mount body, which comprises an upper fitting 202 and a lower fitting 204 of plate shape, and a pair of rubber mount elements 206 of block shape, sandwiched above and below therebetween.
The upper fitting 202 and the lower fitting 204 each bend in a sloping configuration at both the left and right side portions in the drawings, with the rubber mount elements 206 of block shape sandwiched between the sloped portions 202A, 204A and integrally vulcanization bonded to the upper fitting 202 and the lower fitting 204. The pair of rubber mount elements 206 are disposed in a configuration overall that widens out towards the bottom, resembling inverted rabbit ears.
With the upper fitting 202 fastened to the engine side and the lower fitting 204 to the vehicle body side, the mount body 200 elastically supports the engine load with the pair of rubber mount elements 206. As illustrated in FIG. 10B, a through-hole 208 is provided in the upper fitting 202 at a location between the pair of rubber mount elements 206, 206, and a vibration damping bushing 210 constituted as a separate element from the mount body 200 is integrally mounted therein. More specifically, a round tube fitting 212 is affixed to the inside rim of the through-hole 208, and the vibration damping bushing 210 is press-fit into this round tube fitting 212 and thereby mounted fixedly onto the mount body 200.
The vibration damping bushing 210 comprises an inner tube fitting 214 and an outer tube fitting 216. A bushing rubber 218 integrally vulcanization bonded to these and linking the inner tube fitting 214 and the outer tube fitting 216 in the diametrical direction, with the outer tube fitting 216 press-fit into the round tube fitting 212. This vibration damping bushing 210 is also integrally fastened to the lower fitting 204, with the lower end of the inner tube fitting 214 placed in abutment with the lower fitting 204, by means of a fastening arrangement consisting of a bolt 219 passed through the inner tube fitting 214 and a nut 220 threaded thereon. Accordingly, in the vibration damping bushing 210, the inner tube fitting 214 moves in unison with the lower fitting 204, in association with which the bushing rubber 218 undergoes elastic deformation.
FIG. 10A, 222 denotes a stopper fitting of plate shape, secured against the upper end face of the inner tube fitting 214 in the drawing by means of the bolt 219 and the nut 220; vertical stopper action is afforded by means of this stopper fitting 222 and a rubber stopper portion 224—consisting of a corresponding rubber flange portion of the bushing rubber 218—being positioned abutting one another in the vertical direction.
In this example, hollow portions (recesses) 226 that extend in the axial direction are formed in the bushing rubber 218, to the left and right sides of the inner tube fitting 214 in the drawing (which represents the left and right sides of the vehicle body). That is, the hollow portions 226 divide the bushing rubber 218 in the left-right direction of the vehicle body. On the other hand, no hollow portions are disposed to the front and back of the inner tube fitting 214, so that the inner tube fitting 214 and the outer tube fitting 210 are linked directly by the bushing rubber 218.
In the vibration damping bushing 210 of this form, on the basis of rubber elasticity of the vibration damping bushing 210, and specifically the bushing rubber 218, in the front-back direction, it is possible to compensate for the low spring constant (insufficient spring rigidity) in the same direction in the mount body 200, and thus to correct the spring ratio of the spring constant in the vertical direction to the spring constant in the front-back direction.
In the case of the engine mount depicted in FIGS. 10A and 10B, however, the vibration damping bushing 210 is constituted as a separate element from the mount body 200 and is subsequently attached thereto to produce an integral assembly; accordingly, two vulcanization molded parts, i.e. the mount body 200 and the vibration damping bushing 210, are needed as constituent parts for the engine mount, so that there are more parts and an associated increase in cost, and during production of the engine mount it will also be necessary to assemble the vibration damping bushing 210 with the mount body 200, resulting in an increased number of production steps overall, as well as increased cost due to the increase in the number of steps.
In view of the above, the Applicant, in JP-A-9-89046 given below, has proposed an engine mount wherein the mount body and the vibration damping bushing are integrally vulcanization molded; and in particular an engine mount wherein a pair of rubber mount elements of block shape and a bushing rubber are integrally vulcanization molded during vulcanization in a condition of being connected together. In the case of the engine mount taught in JP-A-9-89046, it is possible to constitute the mount body and the vibration damping bushing, which in the past were separate vulcanized components, as a single vulcanized component, and to accordingly reduce the number of vulcanized components required; and additionally to eliminate the subsequent assembly step, thus affording the advantage of reduced cost of the engine mount.
However, subsequent research has shown that where the rubber mount elements and the bushing rubber are integrally molded in this way, there is a risk that the bushing rubber, i.e. the vibration damping bushing, will lack adequate durability. In the case of the engine mount of FIGS. 10A and 10B taught in JP2001-3987, i.e. where the mount body 200 and the vibration damping bushing 210 are constituted as separate vulcanized components, it is possible for the rubber material of the rubber mount elements 106 to differ from the rubber material of the bushing rubber 218, so that the rubber hardness of the bushing rubber 218 can be made greater than the rubber hardness of the rubber mount elements 206. With this arrangement, it becomes possible, for example, to increase spring rigidity in the aforementioned front-back direction, and to thereby suppress deformation of the bushing rubber 218 in the same direction, to afford better durability thereof.
On the other hand, where an engine mount is integrally molded from rubber mount elements and a bushing rubber as taught in JP-9-89046, there is no choice but to fabricate the rubber mount elements and the bushing rubber of the same rubber material. In such instances, it is not possible to set the rubber hardness of the bushing rubber to appropriate hardness as needed, and as a result there is the problem that the spring rigidity (spring constant) of the bushing rubber in the front-back direction, i.e. the spring constant of the entire engine mount in the front-back direction, tends to be insufficient, and the bushing rubber tends to undergo appreciable deformation (compressive elastic deformation) in the same direction, as a result of which the durability of the bushing rubber is diminished.
While the preceding discussion pertains to increasing spring constant in the front-back direction by means of the bushing rubber, there are also instances in which it is necessary to have a high spring constant in the left-right direction of the vehicle, for the purpose of limiting displacement in the left-right direction of a sports car or the like; when a bushing rubber is subjected to compressive elastic deformation in the left-right direction, the problem of diminished durability of the bushing rubber in the same direction will occur.